Rotor for a high speed induction type AC motor having a press fit stacked core

ABSTRACT

A rotor 14 for a high speed induction type ac motor having a construction such that the rotor is provided with an iron core 20 provided, at the periphery thereof, with a plurality of through-bores 22 in which electro-conductive rods 24 made of aluminum rod members are forcibly inserted in a press-fitting manner so as to form opposite projections from the axial opposite ends of the iron core 20, electro-conductive end rings 26 connected to the projections of the electro-conductive rods 24, and slitted pins 30 press-fit in small blind bores 32 formed in the projections of the electro-conductive rods 24 to thereby fixedly attach the electro-conductive rings 26 to the opposite end faces of the iron core 20.

TECHNICAL FIELD

The present invention relates to a rotor for a high speed induction typeac motor. More particularly, it relates to rotor for a high speedinduction type ac motor, provided with an iron core being a stackedassembly of laminations made of plates of magnetic material such as asilicon steel, with a plurality of axial through-bores formed in theperiphery thereof. Electro-conductive rods made of aluminum rods arepressed in the plurality of bores of the iron core so as to be fixedtherein, with ends protruding from opposite ends of the iron core.Electro-conductive end rings are arranged at the opposite ends of theiron core so as to be mechanically engaged with and electricallyconnected to the electro-conductive rods. Slitted tubular pins areforcibly fit in blind bores formed at the opposite ends of theelectro-conductive rods so that elastic extension of the pins ensuresrigid and fixed connection between the ends of the electro-conductiverods and the electro-conductive end rings.

PRIOR ART

A conventional high speed induction type ac motor, especially aninduction type ac motor incorporated in a machine tool as a rotary drivesource for providing the spindle of the machine tool with high speedrotation, typically has a rotative rotor having a construction such thatthe stacked iron core of the rotor is formed with a plurality of slots,and end portions filled with aluminum by a die-casting, or squeezecasting method. The cast aluminum functions as electrical conductors ofthe rotor when magnetic flux passes through the iron core.

when the aluminum is cast in the slots and the end portions of an ironcore by the die-casting or squeeze casting method, the iron core is putin place in a metallic mould into which aluminum melt is poured underpressure. Thus, the aluminum cast rotor for an induction type ac motorcan be produced at a considerably high production rate.

Nevertheless, in the rotor construction having therein cast aluminumelectric conductors, the generation of cavities within the cast aluminumcannot be avoided. Therefore, when the rotor is rotated at a high speed,the cast aluminum of the rotor sometimes bursts at portions adjacent tothe cavities, thereby causing electrical and/or mechanical damage to theinduction type motor.

DESCRIPTION OF THE INVENTION

Accordingly, a principal object of the present invention is to improvethe construction of the above-described conventional rotor for aninduction type ac motor.

Another object of the present invention is to provide a rotor for a highspeed induction type ac motor, provided with a construction such thatthe aluminum electric conductors permitting passage of an electriccurrent in response to the passing of the magnetic flux through the ironcore are mechanically assembled in the iron core so as to prevent thegeneration of casting cavities that might occur during the conventionaldie-casting or squeeze casting method.

A further object of the present invention is to provide a rotor for ahigh speed induction type ac motor, in which the rotor is mechanicallyassembled from separately prepared elements, i.e., an iron core,electro-conductive rods or bars made of aluminum bars and press-fit in aplurality of through-bores formed in the periphery of the iron core,annular-shape end rings attached to opposite ends of the iron core so asto be connected to the aluminum electro-conductive rods, and a slittedtubular pin for providing a rigid mechanical connection between thealuminum electro-conductive rods and the end rings in a manner such thatthe connections of the elements are not loosened even under high speedrotation of the rotor in order to prevent deterioration in themechanical and electric performances of the motor.

To achieve the above-mentioned objects, in accordance with the presentinvention, there is provided a rotor for a high speed induction type acmotor having a construction which comprises:

an iron core having a stacked construction and a plurality of axialthrough-bores disposed at peripheral portions thereof so as to piercetherethrough and be equiangularly arranged in a circumferentialdirection thereof;

a plurality of electrically conductive rod-like members inserted in anddisposed in the plurality of axial through-bores of said stacked ironcore; each of said plurality of electrically conductive rods or bar-likemembers having both ends projecting outward from opposite axial endfaces of said stacked iron core, respectively;

electrically conductive annular end rings; each having an axial boretherein to be engaged with each of said ends of each of said pluralityof electrically conductive rod or bar-like members and fit in said bothaxial ends of said stacked iron core, and;

elastically expandable and shrinkable connecting members, each beingadapted so as to fit in a blind bore of said each end of said pluralityof electrically conductive rods or bar-like members, thereby rigidlyconnecting said electrically conductive end ring to said end face ofsaid stacked iron core.

The above-mentioned elastically expandable and shrinkable connectingmembers may be slitted tubular pin members, which are commonlyavailable. The slits of each pin member are able to exhibit theexpandable and shrinkable property so as to provide a rigid mechanicalconnection between different members.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will be made apparent from the ensuing description of thepreferred embodiment in conjunction with the accompanying drawingswherein:

FIG. 1 is a longitudinal cross-sectional view schematically illustratingthe construction of a high speed induction type ac motor provided with arotary element, i.e., a rotor according to the present invention;

FIG. 2 is an end view taken along the line 2--2 of FIG. 1;

FIG. 3A is a perspective view of a slitted tubular pin used forassembling the rotor according to the present invention;

FIG. 3B is a partial explanatory view of an end of an electro-conductiveannular ring of a rotor, illustrating the connecting operation exhibitedby the expandable slitted tubular pin pressed in an aluminumelectro-conductive rod; and

FIG. 4 is an exploded view of elements for assembling the rotor, such asthe aluminum electro-conductive rods, the electro-conductive end ring,and the slitted tubular pins.

The Best Mode of Carrying out the Invention

Referring to FIGS. 1 and 2, a high speed induction type ac motorprovided with, as a rotary element thereof, a rotor having amechanically assembled construction according to the present inventionhas a rotor 14 arranged inside a cylindrical bore of a stator 12 shownby a chain line, via a gap G. The rotor 14 includes an iron core part 18and a shaft 16. The latter shaft 16 is rotatably supported by rotarybearings (not shown in the drawings) held by a housing (not shown).

The construction of the iron core part 18 of the rotor 14 is differentfrom that of the conventional iron core part having aluminum electricconductors cast by the die-casting or squeeze casting method, and isprovided with a iron core 20 assembled by stacking a plurality oflaminations made of magnetic steel plates, a plurality ofelectro-conductive rods 24 made of aluminum rods and press-fit in aplurality of axial through-bores formed in the periphery of the ironcore 20, electro-conductive annular end rings 26, 26 attached to theaxial opposite ends of the iron core 20, and slitted tubular pins 30connecting the opposite ends of the aluminum electro-conductive rods 24and both electro-conductive rings 26.

The iron core 20 in the form of stacked laminations is provided with aplurality of through-bores 22 formed in the peripheral portion thereofso as to be arranged in the circumferential direction at a predeterminedspacing. Namely, when respective laminations are produced by stampingfrom a raw material of a magnetic steel plate, the through-bores 22 aresimultaneously formed. Thus, when the laminations are stacked to form aniron core, the iron core is provided with the through-bores 22 extendingin the lamination stacking 30 direction, i.e., in the axial direction.The through-bores 22 of the iron core 20 are provided for permittingfilling of electro-conductive material therein, which is indispensablefor constructing an ac induction type motor.

The through-bores 22 of the lamination-stacked iron core 20 is thereforefilled with electro-conductive rods 24; each being made of an aluminumrod having a diameter slightly larger than that of the through-bore 22.The electro-conductive aluminum rods 24 having a predetermined lengthlonger than an axial width of the iron core 20 are forcibly press-fitinto the through-bores 22 from one end of the iron core 20 until theends of the electro-conductive aluminum rod 24 are projected outwardfrom the opposite ends of the iron core 20. The projected ends ofrespective electro-conductive aluminum rods 24 are engaged incorresponding bores 32 of electro-conductive end rings 26, 26 preferablymade of aluminum material so as to fixedly attach both end rings 26 tothe end of the iron core 20.

When the electro-conductive end rings 26, 26 are fixedly attached to theend faces of the iron core 20, slitted pins 30 are then forcibly fit insmall axial blind bores preliminarily formed at the opposite ends ofrespective electro-conductive aluminum rods 24. The slitted pins 30 aremade of a tubular pin having an axial slit, respectively, and an outerdiameter thereof is made larger than an inner diameter of the blind boreof the electro-conductive aluminum rod 24, and therefore when theslitted tubular pins 30 are forcibly inserted in the small blind boresof the electro-conductive aluminum rods 24, the slitted tubular pins 30are pressurized and shrink radially. Accordingly, the slitted pins 30exhibit an elastically expanding force that is resistant against theabove-mentioned pressure so as to provide the electro-conductivealuminum rods 24 with a radial pressure by which the ends of theelectro-conductive rods 24 are pressed against the electro-conductiveend rings 26, 26 to establish a rigid mechanical connection between therods 24 and the rings 26. The rigid mechanical connection brings about acondition such that the electro-conductive rods 24 are in completecontact with the electro-conductive end rings 26, 26, and accordingly,an electrical connection with a reduced electrical resistance is alsoestablished therebetween.

FIG. 3A illustrates the construction of the above-mentioned slittedtubular pin 30 that is a mechanical connecting tubular member having anaxial slit 33 on the outer circumference thereof. The slitted pins 30per se may have various diameters, and are generally made of steelmaterial capable of exhibiting an elastically expanding and shrinkingproperty in the radial direction. The slitted steel pins per se andcommonly available, but according to the present invention, the slittedpins 30 are used for a particular purpose, i.e., for assembling a rotorof an electric motor.

FIG. 3B illustrates how the slitted tubular pins 30 are capable ofproviding a rigid mechanical connection between the ends of theelectro-conductive aluminum rods 24 and the electro-conductive end rings26. Namely, it illustrates that when the slitted pin 30 is forciblyinserted into the above-mentioned small blind bore 34 of the end of theelectro-conductive rod 24, radial pressure acts on the inner wallsurface of the small blind bore 34 of the electro-conductive aluminumrods 24, and therefore the electro-conductive aluminum rod 24 is pressedagainst the corresponding bore 32 of the electro-conductive end ring 26so as to provide a fixed connection between the electro-conductive rodand end ring 24 and 26. Thus, the electro-conductive rods 24 and theelectro-conductive end rings 26 are brought into close contact with oneanother so as to make electrical resistance therebetween as small aspossible. As a result, the electro-conductive rods 24 and the end rings26 can form an electric conductor with a small stable electricresistance during the operation of an induction type ac motor.

FIG. 4 illustrates the assembling process of the rotor in which theprojections 24a of the opposite ends of the electro-conductive rods 24are rigidly connected to the end rings 26 by using the slitted tubularpins 30. Namely, the projections 24a of respective electro-conductivealuminum rods 24 are engaged in the bores 32 of the end rings 26 andformed with axial blind-bores 34 for permitting the slitted pins 30 tobe forcibly fit therein. The fitting of the slitted pins 30 in theblind-bores 34 of the rods 24 are implemented after the assembly of theend rings 26 and the rods 24.

From the foregoing description, it will be understood that, inaccordance with the present invention, the rotor 14 for an inductiontype ac motor can be constructed by not using a die-casting of aluminummaterial. Accordingly, since the rotor 14 does not have any castingcavities in the aluminum parts thereof, the aluminum parts do not burstowing to the existence of cast cavities in the aluminum material withthe rotor assembled in accordance with the present invention even whenit is rotated at a high speed. Therefore, the rotor according to thepresent invention eliminates the problems of the prior art, i.e., themechanical breakage and deterioration in the electrical performanceencountered by the rotor for an induction type ac motor of the priorart.

Particularly, the slitted tubular pins 30 are axially fit in theelectro-conductive rods, and accordingly, when the rotor is rotated at ahigh speed, the slitted pins are not subjected to centrifugal force.

It should be understood that the connecting force exhibited by theslitted pins when they are forcibly fit in the electro-conductive rodsshould be adjusted to an appropriate level. Thus, the mechanicaldimensions of the pins and the material from which the slitted pinsshould be made so that they are selected depending upon the outerdiameter of the electro-conductive rod and the diameter of the smallblind bores thereof.

In accordance with the present invention, a rotor for a high speedinduction type ac motor is provided with mechanically assembled aluminumparts, and is not provided with cast aluminum portions therein, andaccordingly, even when the rotor rotates at a high speed, the aluminumparts of the rotor do not burst owing to the fact that there are nocasting cavities therein. Thus, high speed rotation of the rotor can besafely realized.

Further, in the construction of the rotor according to the presentinvention, connection of the electro-conductive rods assembled in theiron core to the electro-conductive end rings is achieved by using theslitted tubular pins capable of constantly exhibiting a strongconnecting force on the basis of the expanding and shrinking property ofthe slitted pins. Therefore, the mechanical strength of the connectiondoes not deteriorate over a long operational life of the motor, andaccordingly, the electrical resistance at the connection is notincreased for the long operational life of the motor. Consequently, bothmechanical and electrical performances of the high speed induction typeac motor are constantly maintained so as to provide a considerablyreliable high speed induction type ac motor capable of being used as arotary drive source of a machine tool spindle.

Moreover, assembly of the rotor can be easily effected by theutilization of the slitted tubular pins which are commonly available,and therefore the rotor can be manufactured at a low cost.

We claim:
 1. A rotor for a high speed induction type ac motorcomprising:an iron core having a stacked construction and a plurality ofaxial through-bores piercing therethrough and equiangularly arranged ina circumferential direction thereof; a plurality of electricallyconductive rod-like members inserted in and disposed in the plurality ofaxial through-bores of said stacked iron core; each of said plurality ofelectrically conductive rod-like members having both ends projectingoutward from both axial end faces of said stacked iron core,respectively; electrically conductive annular end rings, each having aplurality of axial bores therein, each of said axial bores to be engagedwith corresponding ends of each of said plurality of electricallyconductive rod-like members and fit in said both axial ends faces ofsaid stacked iron core, and; elastically expandable and shrinkableconnecting members, each being adapted to be fit in a blind bore of saideach end of said plurality of electrically conductive rod-like members,thereby rigidly connecting said electrically conductive end ring to eachof said end faces of said stacked iron core.
 2. A rotor for a high speedinduction type ac motor according to claim 1, wherein said electricallyconductive annular end rings are made of an aluminum material.
 3. Arotor for a high speed induction type ac motor according to claim 1,wherein each of said plurality of electrically conductive rod-likemembers is made of an aluminum rod.
 4. A rotor for a high speedinduction type ac motor according to claim 1, wherein each of saidelastically expandable and shrinkable connecting members comprises aslit pin member.
 5. A rotor for a high speed induction type ac motoraccording to claim 1, wherein said stacked iron core is provided with ashaft member fixedly mounted therein, and rotatably arranged inside astator of said ac motor.
 6. A rotor for a high speed induction type ACmotor according to claim 1, wherein said elastically expandable andshrinkable connecting members have a cylindrical cross-section, andwhere each of said blind bores of said plurality of electricallyconductive rod-like members is correspondingly cylindrical such thatsaid elastically expandable and shrinkable connecting members fit insaid blind bores.